Couplings for joining pipes together end to end comprise arcuate segments that circumferentially surround co-axially aligned pipes and engage circumferential grooves positioned proximate to the ends of each pipe. The couplings are also used to connect pipes to fluid control components such as valves, reducers, strainers, restrictors, pressure regulators, as well as components to components. Although in the description which follows pipes are described, they are used by way of example only, the invention herein not being limited for use only with pipes per se. It should also be noted that the term “pipe” as used herein refers to straight pipes as well as elbows, tees and other types of fittings.
The segments comprising the couplings have circumferential keys that extend radially inwardly toward the pipes and fit within the grooves around the pipes. The keys are typically somewhat narrower than the grooves to permit them to fit within the grooves and bear against the shoulders formed by the grooves to hold the pipes together against internal pressure and external forces that may be applied to the pipes. External forces may arise due to thermal expansion or contraction of the pipes due to changes in temperature as well as the weight of the pipes or components such as valves attached to the pipes, which can be significant for large diameter pipes and valves. Wind loads and seismic loads may also be a factor.
It is advantageous that pipe couplings be substantially rigid, i.e., resist rotation of the pipes relative to one another about their longitudinal axes, resist axial motion of the pipes relatively to one another due to internal pressure, and resist angular deflection of pipes relative to one another. A rigid coupling will be less likely to leak, requiring less maintenance, and will simplify the design of piping networks by eliminating or at least reducing the need for engineers to account for axial motion of pipes in the network when subjected to significant internal pressure. Pipes joined by rigid couplings require fewer supports to limit unwanted deflection. Furthermore, valves and other components which may tend to rotate out of position because their center of gravity is eccentric to the pipe axis will tend to remain in position and not rotate about the longitudinal axis under the pull of gravity when the pipe couplings are substantially rigid.
Many couplings according to the prior art do not reliably provide the desired degree of rigidity mainly because they use keys having rectangular cross-sections that are narrower than the width of the grooves that they engage. This condition may result in inconsistent contact between the coupling and the pipes which allows too much free play and relative movement, for example, axially, rotationally or angularly, between the pipes. It is also difficult to ensure that such keys properly engage the grooves. Couplings which provide a more rigid connection may be ineffective to force the pipe ends apart at a desired distance from one another so that the keys and grooves are in proper alignment and the pipes are properly spaced. When properly spaced apart, the pipe ends and the coupling cooperate with a sealing member positioned between the coupling and the pipe ends to ensure a fluid tight seal. The movement of the pipes, although small, is effected as the couplings are engaged with each other and the pipe and may required that significant torque be exerted upon the fasteners used to clamp the coupling to the pipes. This is especially acute when pipes to be joined are stacked vertically one above another, and the action of engaging the coupling with the pipes must lift one of the pipes upwardly relatively to the other in order to effect the proper spacing between the pipe ends. For such couplings, it is also difficult to reliably visibly ensure that the couplings have been properly installed so that the keys engage the grooves and the pipes are spaced apart as required to ensure a fluid tight seal.
It would be advantageous to provide a coupling that provides increased rigidity while also reducing the force necessary to engage the coupling with the pipe ends to effect their proper spacing, and also provides a reliable visual indication that the couplings are properly installed on the pipes.